1. Field of the Invention
The present invention relates to a fuel properties detecting apparatus for an internal combustion engine to detect the properties of fuel such as alcohol mixed with gasoline to be supplied to the internal combustion engine.
2. Discussion of Background
Various types of apparatus for detecting the properties of fuel have been known. Most such apparatuses are of a type which uses an alcohol sensor. There are few conventional apparatuses or methods without using the alcohol sensor.
As an example of a method of detecting the properties of fuel, description concerning Japanese Unexamined Patent Publication 78480/1985, which discloses a technique close to the present invention although it concerns a technique of ignition timing control, will be made.
FIG. 7 is a block diagram of a fuel properties detecting apparatus used for a conventional fuel properties detecting method, and FIG. 8 is a diagram showing major parts of the apparatus used for the conventional fuel properties detecting method.
In FIG. 8, a reference numeral 5 designates a cylinder block of engine, numeral 22 designates a knocking sensor attached to the block 5, a numeral 11 designates an ignition plug, a numeral 24 designates a distributer, a numeral 25 designates a crank angle sensor, a numeral 25 designates a control device, a numeral 4 designates an intake manifold, a numeral 12 designates an air-flow sensor, a nemeral 23 designates an igniter and a numeral 10 designates a fuel injection valve.
A basic operation in the conventional apparatus will be described.
As shown in a block diagram in FIG. 7, a knocking sensor A detects vibrations of pressure in an engine caused during combustion. A knocking level discriminating means B discriminates presence or absence of a knocking on the basis of a signal generated from the knocking sensor A. A lag angle control means C controls a lag angle in ignition timing when a knocking occurs. A lead angle control means D controls to advance the ignition timing when there occurs no knocking. A property change detecting means F detects change in a knocking generation level corresponding to an advanced angle in ignition timing. A maximum lag angle limit operating means G operates the maximum limit value of a lag angle provided from the lag angle control means C on the basis of change in properties detected by the property change detecting means F. The above-mentioned means constitute an ignition timing control apparatus.
The operation of the ignition timing control apparatus will be described.
The ignition timing control apparatus is operated in such a manner that when the property change detecting means F detects a change in properties of knocking generation level corresponding to an amount of lead angle in ignition timing, determination of the properties of fuel, for instance, whether gasoline used for the engine is regular gasoline for a high octane gasoline, is made. Then, the maximum lag angle limit operating means G determines the maximum limit value of lag angle by the lag angle control means C, whereby the optimum value is operated. When the knocking level discriminating means B judges that there is a knocking, the knocking level is maintained by causing an angle of ignition timing to be lagged to the maximum limit value. FIG. 9 shows change in properties of a knocking generating level corresponding to an amount of lead angle in ignition timing, which changes depending on a kind of gasoline, such as regular gasoline or a high octane gasoline.
In FIG. 9, a broken line indicates a relation of a torque to a knocking level when the regular gasoline is used and solid line shows a relation of them when the high octane gasoline is used.
Now, assuming that regular gasoline is used. When a predetermined basic ignition timing is at a point B, the knocking level corresponding to the point D becomes a trace level. However, when a high octane gasoline is used while the basic ignition timing is kept unchanged, there takes place no knocking at all, and when the ignition timing is advanced to a point C, the knocking level becomes the trace level. In other words, there can be found the properties of fuel of either regular gasoline or a high octane gasoline by detecting the change of knocking generation level with respect to the lead angle quantity of ignition timing.
Generally, it is well-known that an octane value is changed by mixing alcohol in gasoline. In consideration of the above-mentioned fact and the change of knocking generation level with respect to the lead angle quantity, presence or absence of alcohol in gasoline can be detected by the knocking sensor 22 for detecting a knocking level change. Namely, when the output of the knocking sensor 22 is supplied to a filter having a knocking frequency as a cut-off frequency or the frequencies of higher harmonics in order to examine the magnitude of the output with respect to the lead angle quantity in ignition timing, the magnitude of the output is small when some amount of alcohol is mixed with gasoline and the same ignition timing is used. Accordingly, by previously determining the ignition timing in a level such as K1 or K2, absence or presence of alcohol in gasoline can be detected by a knocking level change.
In the conventional fuel properties detecting apparatus having the above-mentioned construction, it was impossible to detect the properties of fuel unless a knocking takes place. Further, it was impossible to detect quantitatively the content of alcohol in gasoline.